1. Field of the Invention
The invention relates to a method of recording and reproducing content information and supplemental information relating thereto, in which method an encoded signal representing the content information and a watermark pattern representing the supplemental information are recorded.
The invention further relates to a method of encoding content information and supplemental information relating thereto, in which an encoded signal is generated by encoding the content information in accordance with a watermark pattern representing the supplemental information.
The invention further relates to a method of retrieving supplemental information related to content information, in which a watermark pattern representing the supplemental information is retrieved from an encoded signal representing the content information and the watermark pattern.
The invention further relates to a system for recording and reproducing content information and related supplemental information, an arrangement for generating an encoded signal, an arrangement for processing an encoded signal, an encoded signal, a control signal and a record carrier.
2. Description of the Related Art
Such methods and such a system are described in patent application WO 97/13248 (PHN 15391), document D1 in the list of related documents. The document notes, that video and audio content information is increasingly being recorded in a digitally encoded form, for example, an MPEG bitstream. There is a growing need to transfer supplemental information logically related to the content information, which supplemental information is intended for controlling the processing of the content information. The supplemental information should be protected against manipulation in order to remain in command of the controlling function. Supplemental information is particularly useful in copy protection applications.
Copy protection has a long history in audio publishing. The presently installed base of equipment, including PC's with audio cards, provide little protection against unauthorized copying. In any copy-protection scheme, the most difficult issue is that a pirate can always attempt upon playback of an original disc, to treat the content as if it were an analog home recording and record it. It is desirable that consumer recorders be able to copy recordings of the consumer's own creative productions without any limitation, but prohibit the recording of copy-right material. Thus, the copy protection mechanism must be able to distinguish between consumers' own creations and content that originates from professional music publishers. The equipment must make this distinction based on the audio or video signal only, as any reference to the physical source of content (e.g. disc or microphone) is unreliable. For digital storage media such as DCC, "copy bits" have been defined, which bits indicate a copyright status, e.g. "no copy allowed", "free copy" or "one generation of copy allowed". Other copy bits may indicate that the medium containing the information is a "professional" medium manufactured by pressing and is not a "recordable" disc.
Marking the digital content signal, for example by a marker accommodated in such an encoded signal so as to classify the encoded signal as authentic programme material, is referred to as watermarking. In our system the watermark takes the form of a multi-bit pattern representing some supplemental information, e.g. indicating that the encoded signal constitutes copy protected content and/or indicate the origin of the content. A watermark usually has a fixed part to identify the bit pattern as a valid watermark and/or synchronising the retrieval process, and may comprise a variable part representing said supplemental information. A method is disclosed in D1 for embedding the watermark pattern in the encoded signal such that it is easy to detect, but difficult to erase or modify without serious degradation of the quality of the audio or video content after decoding. Moreover, the watermark pattern has to be relatively long to prevent an unmarked, encoded signal from being classified accidentally as marked. Also the watermark should be detectable in a relatively short time, e.g. 1 to 10 seconds, to enable a fast response when classifying a signal. Known watermarks have the disadvantage that they represent only a limited amount of supplemental information. Manipulation of (parts of) the watermark by a malicious party is still possible with only a limited degradation of the content after decoding.